Argon Ion Milling Research Articles

C-Axis Current-voltage Characteristics of Mesa Structures on Bi2Sr2CaCu2O8+δ Single Crystals Fabricated by a Simple Technique Without Photolithography

A simple technique is reported for fabricating the mesa structure on Bi2Sr2CaCu2O8+δ single crystal. In the patterning process, metal masks are used instead of photolithography and argon ion milling is applied to form the small mesa on the Bi2Sr2CaCu2O8+δ crystal surface. Real four-probe transport measurements are made on the mesa structure and typical c-axis current-voltage (I - V) characteristics of the intrinsic Josephson effect have been observed. The superconducting gap parameter can be extracted from the multi-branch structure in the I - V characteristics. Additionally, from the strong hysteresis in the I - V characteristics, the capacitance CJ of the unit intrinsic Josephson junction has been estimated to be 2.3 pF, which is in good agreement with that evaluated from the geometric parameters of the unit junction between the two copper oxide layers.

Fabrication of suspended piezoelectric microresonators

A new process for realizing piezoelectric microdevices has been developed. Suspended piezoelectric clamped-clamped beam resonators have been fabricated using sol-gel deposited lead zirconate titanate (PZT) films as the piezoelectric material, platinum (Pt) as the top and bottom electrode, and silicon dioxide for the supporting beam structure. A five-mask process was used to fabricate the suspended resonators. The process flow included sol-gel PZT deposition, Pt sputter deposition, Pt and PZT argon ion milling, PZT wet and reactive ion etching (RIE), silicon deep reactive ion etching (DRIE), and oxide RIE. Both single-and triplebeam resonators were fabricated with beam widths of 15, 20, and 30 um and lengths of 200 and 400 um. Testing of the resonators produced resonant frequencies between 100 kHz and 1.2 MHz, depending on beam geometry.

Microstuctural Characterization of Water-Rich Boehmite (AlO(OH)): TEM Correlation of Apparently Divergent XRD and TGA Results

An understanding of the solid-phase thermodynamics and aqueous speciation of aluminum is critical to our ability to understand and predict processes in a wide variety of geologic and industrial settings. Boehmite (AlO(OH)) is an important phase in the system Al2O3-H2O that has been the subject of a number of structural and thermodynamic studies since its initial synthesis [1] and discovery in nature [2]. Unfortunately, it has long been recognized that thermogravimetric analysis (TGA) of both synthetic and natural boehmite samples (that appear well crystallized by powder XRD methods) yields significant excess water - typically losing 16-16.5 wt. % on heating as compared with a nominal expected weight loss of 15.0 wt. % [3,4]. The boehmite used in our experiments was synthesized hydrothermally from acid-washed gibbsite (Al(OH)3) at 200°C. Powder XRD and SEM examination showed no evidence of the presence a contaminant phase. The TGA patterns do not suggest that this is due to adsorbed water, so a structural source is likely. We therefore undertook to examine this material by TEM to clarify this phenomenon.Boehmite is orthorhombic (a = 0.0285nm, b = 0.1224nm and c = 0.0365nm, Amam). The crystals were tabular with major surfaces normal to <010>. Simple powder dispersals onto holey carbon films typically resulted in b-axis orientations parallel to the electron beam. To view other orientations, specimens were mulled in M-Bond epoxy, pressed between plates of single-crystal Si (aligning the boehmite tablets parallel to the Si plates) while the epoxy cured. Electron transparent thin foils normal to the silicon plates were produced by argon ion milling techniques. Sample stability in the electron beam was dramatically improved by cooling to −140°C using an 2 cold stage.

Side-wall damage in a transmission electron microscopy specimen of crystalline Si prepared by focused ion beam etching

In focused ion beam (FIB) fabrication of cross-sectional transmission electron microscopy (X-TEM) specimens, highly accelerated ion beams sometimes cause serious damage. The damage can be induced in both the specimen surface and the side walls. We used the X-TEM technique to investigate the sidewall damage in crystalline Si. The damaged layer was found to be about 20 nm thick in the case of 30-keV-FIB etching. We evaluated several techniques for reducing the damage, such as gas-assisted etching (GAE) with iodine, low-energy FIB etching, and cleaning by broad argon ion milling or by wet etching. The damage depth was 19 nm for GAE and 10 nm for 10 keV FIB etching, and was reduced to 7 nm by 3 keV argon ion milling with a beam current of 20 μA and a tilt angle between the beam and the specimen of 4°. Wet etching using a mixture of nitric and hydrofluoric acid removed most of the damaged layer. The effect of the damaged layer on TEM observation was also investigated, and it was shown that removal of the damaged layer results in a high-resolution TEM image.

Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+δ/ intrinsic Josephson junctions fabricated by a simple technique without photolithography

Due to the roughness in the surface of the crystal sample, it is hard to use photolithography in the patterning process of the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic Josephson junction. In this paper, we report a simple technique for fabricating the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic Josephson junctions. In the patterning process, metal masks are used instead of photolithography and argon ion milling is applied to form a small mesa on the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// crystal surface. Real four-probe transport measurements are made on the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// intrinsic junctions and typical current-voltage characteristics with multi-branch structure have been observed, from which the superconducting gap parameter can be extracted. Additionally, from the strung hysteresis in the I-V characteristics, the capacitance C/sub J/ of the unit intrinsic Josephson junction can be estimated, which is in good agreement with that evaluated from the geometric parameters of the unit junction between the two copper oxide lagers.

DNA bound to polypyrrole films: high-resolution imaging, DNA binding kinetics and internal migration

We have studied the time-dependent uptake of 35S radiolabeled DNA with electrochemically prepared polypyrrole films. The two distinct polypyrrole film surfaces, a rough (solution polymeric growth face, R) and a smooth surface (electrode face, S) were characterized by low-resolution AFM and high-resolution transmission electron microscopy (TEM). These studies showed the presence of steep contours and defects in the form of large and small surface holes and valleys on the rough surface of polypyrrole. The void dimensions ranged from the nanoscale to micron size. By contrast, the smooth surface was flatter and largely devoid of significant structural defects and exhibited closer packing of the polypyrrole chains over large areas. Both surfaces were comprised largely of chains whose average diameters were 1.0–1.2±0.3 nm. The surface characterization studies were complemented by time-dependent DNA uptake studies which showed a t 1/2-dependent total uptake of 35S DNA at higher levels on the rough surface compared to the smooth surface. This is consistent with the apparent higher effective surface area of the rough surface compared to the smooth. Using a proportional counter the time-dependent ratio (R/S) of the 35S DNA detected from the rough surface of the polypyrrole disk to that detected from the smooth surface suggested that DNA was migrating into the disk interior from its uptake surface. The rough side defect dimensions measured by TEM were more than sufficient to allow for the penetration and migration of DNA into the disk interior. Both R/S ratios were extrapolated and found to intersect at an R/S value close to 1.0, suggesting a kinetic process leading ultimately towards a nearly uniform radiolabeled DNA distribution in the disk. These kinetic results were in agreement with the surface characterization studies and suggest a model in which sizeable internal pores exist throughout the electrochemically prepared polypyrrole, that could account for the DNA migration effect. This was confirmed by TEM of the interior of a polypyrrole disk produced by Argon ion milling.

Transmission electron microscope specimen preparation of Zn powders using the focused ion beam lift-out technique

Particles of Zn powder have been studied to show that high-quality scanning electron microscope (SEM) and transmission electron microscope (TEM) specimens can be rapidly produced from a site-specific region on a chosen particle by the focused ion beam (FIB) lift-out technique. A TEM specimen approximately 20-µm long by 5-µm wide was milled to electron transparency, extracted from the bulk particle, and micromanipulated onto a carbon coated copper mesh TEM grid. Using the FIB lift-out method, we were able to prepare a site-specific TEM specimen from a difficult material in under 3 hours. The TEM analysis of the lift-out specimen revealed a large amount of thin area free from characteristic signs of damage that may be observed as a result of conventional argon ion milling. The overall microstructure of the specimen prepared by the FIB lift-out method was consistent with samples prepared by conventional metallographic methods. A grain size of ∼10 to 20 µm was observed in all specimens by both TEM and SEM analysis. Light optical microscopy revealed the presence of internal voids in ∼10 to 20 pct of all particles. The SEM analysis showed the voids to extend over ∼70 pct of the particle volume in some cases.

Dry Etching of Sol-Gel Pzt

AbstractTwo techniques for dry etching of sol-gel lead zirconate titanate (PZT 52/48) thin films were investigated: reactive ion etching and argon ion milling. Etched profiles were characterized by scanning electron microscopy. For reactive ion etching, a parallel plate etcher was used with HC2ClF4, an environmentally safe etch gas, in a process described by other researchers. Etch rates were measured and compared as a function of electrode shield material (ardel, graphite, alumina) and RF input power (100 to 500 W). These etch rates varied from 10 to 100 nm/min. Reactive ion etched sidewall angles 12° off normal were consistently produced over a wide range of RF powers and etch times, but overetching was required to produce a clean sidewall. For argon ion milling, a 300 mA/500 V beam 40° off normal to the substrate operating in a 72 mPa argon pressure was used. These ion milling conditions produced an etch rate of 250 nm/min with a sidewall slope angle of about 70°. The ion milling etch rate for sol-gel PZT was significantly faster than rates reported for bulk PZT. The 500 nm thick PZT films used in this study were prepared by the sol-gel process that used methoxyethanol solvent, spin coating on t/Ti/SiO2 silicon substrates, and rapid thermal annealing for 30 s at 650 °C for crystallization of the perovskite phase.

Reduction of the Damage Induced in an Fib-Fabricated X-Tem Specimen

AbstractIn focused ion beam (FIB) fabrication of cross-sectional transmission electron microscopy (X-TEM) specimens, highly accelerated ion beams sometimes cause serious damage. The damage can be induced in both the specimen surface and in the side walls. We used X-TEM observations to investigate the side-wall damage induced by FIB fabrication in crystalline silicon. The damaged layer was found to be about 20 nm thick in the case of 30-keV FIB etching. We tried to reduce the damage by several methods, such as gas-assisted etching (GAE) with iodine, broad argon ion milling and wet etching. The damaged layer was 19 nm for GAE and 12 nm for argon ion milling with a beam current of 70 mA and the tilt angle between the beam and the specimen of 15 degrees. Wet etching using a mixture of nitric and hydrofluoric acid removes most of the damaged layer.

Electron Microscopy, Electrical Activity, Artefacts and the Assessment of Semiconductor Epitaxial Growth

AbstractThe characterisation of semiconductor thin films and device structures increasingly requires the use of a variety of complementary electron microscope-based techniques as feature sizes decrease. We illustrate how layer electrical and structural properties can be correlated: firstly averaged over the bulk and then on the individual defect scale, e.g. scanning transmission electron beam induced conductivity can be used to image the recombination activity of orthogonal <110> misfit dislocations within relaxed MBE grown Si/Si1-xGex/Si(001) heterostructures on the sub-micrometre scale. There is also need for improved understanding of sample preparation procedures and imaging conditions such that materials issues relevant to ULSI development can be addressed without hindrance from artefact structures. Hence, we consider how point defects interact under the imaging electron beam and the relative merits of argon ion milling, reactive ion beam etching, focused ion beam milling and plasma cleaning when used for TEM sample preparation. Advances in sample preparation procedures must also respect inherent problems such as thin foil surface relaxation effects, e.g. cleaved wedge geometries are more appropriate than conventional cross-sections for the quantitative characterisation of δ-doped layers. Choice of the right imaging technique for the problem to be addressed is illustrated through consideration of polySi/Si emitter interfaces within bipolar transistor structures. The development of microscopies for the rapid analysis of electronic materials requires wider consideration of non-destructive techniques of assessment, e.g. reflection high energy electron diffraction in a modified TEM is briefly described.

Intrinsic Josephson junctions under microwave irradiation

Small mesa-type junctions around 10 μm lateral size have been realized by argon ion milling on top of high quality Bi 2Sr 2CaCu 2O 8 single crystals and studied in external microwave fields. Although the junction dimensions are much smaller than the magnetic penetration depth they have to be regarded as long junctions since phase variations occur on a smaller scale. A couple of unexpected features in the current-voltage characteristics, including zero current crossings, are most likely understood by coherent vortex flow.

Nanowire bonding with the scanning tunneling microscope

We have developed a reliable lithographic method to pattern thin gold films by locally exposing a thin layer of an electron beam resist with the tip of a scanning tunneling microscope (STM). The exposure of the resist layer is induced by applying a voltage difference of ca. −10 V between the STM tip and the gold film on top of which the resist layer has been deposited with the Langmuir-Blodgett technique. Our resist material is omega-tricosenoic acid which acts as a negative resist. After development, the unexposed areas of the gold film can be removed via argon ion milling. We have been able to obtain continuous gold lines having a width down to 15 nm, the linewidth being determined by the exposure dose. When reducing the tunneling voltage < 5 V, exposure of the Langmuir-Blodgett resist layer no longer occurs and one switches to the classical topographic imaging mode. This switching provides us with the unique possibility to attach electrical contacts to existing nanostructures. As a nice example of this nanowire bonding, gold contacts have been attached to individual multiwalled carbon nanotubes. We have made detailed measurements of the nanotube resistance as a function of temperature down to 10 mK and in magnetic fields up to 14 T. At low temperatures a pronounced negative magnetoresistance is observed which is consistent with the two-dimensional weak electron localization occurring in the cylindrical graphite layers forming the nanotubes. The nanotubes also show reproducible fluctuations of the magnetoresistance which can be related to the Aharonov-Bohm effect in the nanotubes.

Properties of doped-YBCO bicrystal grain-boundary junctions for Josephson field effect transistor

We report the properties of hole-overdoped and underdoped YBa2Cu3O7−x (YBCO) grain-boundary junctions (GBJ) on the 24° tilt SrTiO3 (100) bicrystals as a function of temperature and junction width. Epitaxial thin films of YBCO, Y0.7Ca0.3Ba2Cu3O7−y (Co-YBCO) were deposited by pulsed laser deposition, and the GBJs were fabricated by standard photolithography with argon ion-milling. We measured the IcRn products of ∼ 1.2 mV for Ca-YBCO and ∼ 0.3 mV for Co-YBCO GBJ at 27 K. Critical current densities(Jc) of the junctions were 1.4×103 and 3.0x104 A/cm2 at 27 K for the Ca- and Co-YBCO GBJs, respectively. This is explained in terms of a weak-link behavior at the grain-boundaries in comparison with the bulk properties of the doped YBCO films.

Tantalum plasma etching with minimum effect on underlying nickel-iron thin film

Removing tantalum (Ta) from nickel-iron (NiFe) surface in CF 4/O 2 plasma was first demonstrated to be a more robust process than argon ion milling in preserving and controlling the NiFe magnetic thickness during Ta overetch. A factorial study showed that the NiFe magnetic thickness loss could be further reduced by replacing CF 4 with CHF 3 and reducing O 2 flow. For an optimized CHF 3/CF 4 process, the NiFe magnetic thickness loss for a 100-Å Ta overetch was only 5 Å. Electron spectroscopy for chemical analysis showed the presence of the fluorocarbon on the CF 4/CHF 3 etched Ta surface and nickel fluoride on the NiFe surface after Ta overetch. A mechanism of removing tantalum with minimum effect on the underlying nickel-iron thin film was also proposed.

X-ray Photoelectron Spectroscopy Depth Profiling of Aluminium Nitride Thin Films

Aluminium nitride thin films grown at room temperature on degenerate silicon (conducting) substrates have been studied using XPS. The hydrolysis layer at the surface of the AIN was examined using valence band measurements, and the effect of 5 kV argon ion milling used to remove the hydrolysis layer was scrutinized using angle-resolved XPS. The N/Al ratios found from the angle-resolved measurements indicate nitrogen depletion from the surface of the milled samples, whereas O/Al ratios indicate no such depletion of oxygen. After argon ion milling, carbon uptake from the ultrahigh vacuum analysis chamber was found to be significant.

Cross-Sectional Tem Sample Preparation of Phase-Change Optical Disk by Ion Milling

AbstractIt is very difficult to prepare cross-sectional TEM samples for phase-change optical disks by conventional argon ion milling because of the difference of ion milling rates between multilayers and the polymer substrate. We have been successful in preparing samples of those optical disks by ion milling method with dissolution of the polymer substrate in advance. The cross-sectional structure was observed more clearly in this method rather than in ultramicrotome method.

Field emission observations from CVD diamond-coated silicon emitters

The self-aligned fabrication of diamond-coated silicon field emitters was performed by a selective chemical vapor deposition of diamond on p-type (100)-oriented silicon followed by argon ion milling of the patterned structures. Field emission measurements of as-prepared and thermally as well as hydrogen plasma treated diamond-coated silicon emitter arrays with base diamters ranged from 1.2 to 10 μm were carried out by field emission scanning microscopy with μm resolution. The applied electrical surface field has been varied between 20 and 250 MV m −1. It was found that the combination of thermal and hydrogen plasma treatments can substantially improve the electron emission of diamond-coated silicon emitters. Depending on their base diameter the field emitters demonstrated stable electron emission for E>80–120 MV m −1. Fowler-Nordheim analysis for arrays and individual field emitters was performed.

Sidewall and surface induced damage comparison between reactive ion etching and inductive plasma etching of InP using a CH4/H2/O2 gas mixture

We report the results of a comparative characterization between reactive ion etching and inductive coupled plasma (ICP) etching of InP with a CH4/H2/O2 gas mixture. Particular attention was paid to the surface morphology and to the pattern profiles that were observed by scanning electron microscopy. A comparison with morphology of patterns etched by argon ion milling is also included. Auger electron spectroscopy and secondary ion mass spectrometry were used to obtain the elemental composition in the top 30 nm of the etched surface and to evaluate pollution and stoichiometry. Transmission electron microscopy was used to observe the sidewall damage and to evaluate the effect of sidewall deposit. The respective roles of incident and reflected energetic species and deposits are identified. The effect of anisotropy on sidewall deposits was also observed. Finally, surface damage induced on InP etched substrates was characterized through photoluminescence intensity. The destructive effects of high ion energy etching processes on the samples was observed in terms of stoichiometry modification, surface contamination, and polycrystallization of sidewalls. Some very low energy processes were studied with the ICP equipment. An extremely low damage level could be obtained in such processes while keeping a sufficient etch rate. However, the low ion energy ICP etching processes are isotropic.

Preparation of TEM plan-view and cross-sectional specimens of ZnSe/GaAs epilayers by chemical thinning and argon ion milling

Clean and even millimetre-size electron-transparent plan-view specimens of ZnSe/GaAs with and without the GaAs substrate completing with a lift-off method for GaAs epilayers have been prepared by chemical thinning with a 5:1 (NaOH:H 2O 2) solution. Cross-sectional specimens of ZnSe/GaAs with very little ion-induced damages and extensive thin area suitable for HREM imaging have been prepared by argon ion milling. Ion-induced damage in ZnSe has virtually been eliminated by progressively decreasing ion voltages to 0.7 kV. Large thin areas result from the glue line of the cross-sectional specimen being shadowed by the GaAs substrate in off-centre single-side ion milling.

The SUPFET, a new photodetector with ultrathin YBaCuO/PrBaCuO multilayer channel

Several electric field effect devices have been built with YBaCuO/PrBaCuO layers and multilayers; The layers are deposited by an inverted cylindrical magnetron sputtering process (ICM) on MgO substrates. This process has been proved to give very good performances even for thinner and ultra thin films. The films used for the field effect transistor devices consist of one or two bilayers of YBaCuO and PrBaCuO with a nominal thickness of each material of about 4 nm. Small channel geometries of 50/spl times/60 microns are etched by argon ion milling and the channel is covered by a silicon dioxide dielectric layer (50-100 nm). The gate contacts as well as the drain and source contacts are made by sputtered gold pads. These devices are tested in static and dynamic measurements: the silicon dioxide layer inhibits symmetric I-V characteristics of the dielectric layer with high breakdown field strength up to 4 MV/cm. The gate capacity of a few pF allows the test of the device in a kHz frequency range. Tests with sine wave gate voltages show low distortion of the output signal with a voltage gain of about 0.01. Smaller dielectric layers could raise the gain close to one. The results of these field effect experiments are compared with optically induced effects. The optical measurements are performed with a helium-neon laser (633 nm) with a power density of 600 W/cm/sup 2/. The laser pulses with frequencies up to 1 MHz give responses somewhat similar to the observed field effect responses. Combining field effect and optical irradiation, it Is found that the laser pulses seem to create charge carriers, screening the field effect. Based on this principle a new photodetector is proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>